The present invention relates generally to devices for transmitting electromagnetic signals of a desired frequency range and more particularly to devices for transmitting electromagnetic signals of a desired frequency range that additionally provide both over-voltage protection to the transmission line and signal filtering capabilities.
A radio frequency (RF) transmission line is a structure that is designed to efficiently transmit high frequency radio frequency (RF) signals. An RF transmission line typically comprises two conductors, such as a pair of metal wires, that are separated by an insulating material with dielectric properties, such as a polymer or air. One type of an RF transmission line which is well known in the art is a coaxial electric device.
Coaxial electric devices, such as coaxial cables, coaxial connectors and coaxial switches, are well known in the art and are widely used to transmit electromagnetic signals over 10 MHz with minimum loss and little or no distortion. As a result, coaxial electric devices are commonly used to transmit and receive signals used in telecommunications, broadcast, military, security and civilian transceiver applications as well as numerous other uses.
A coaxial electric device typically comprises an inner signal conductor which serves to transmit the desired high frequency communication signal between a source and a load. The inner signal conductor is separated from an outer conductor by an insulating material, or dielectric material, the outer conductor serving as the return path, or ground, for the communication signal. Such an electric device is typically referred to as coaxial because the inner and outer conductors share a common longitudinal axis. It should be noted that the relationship of the geometry of the conductors and the properties of the dielectric materials disposed between the conductors substantially define the characteristic impedance of the coaxial device.
It has been found that, on occasion, potentially harmful voltages are transmitted through RF transmission lines. In particular, radios operating in either the lower end of the ultra high frequency (UHF) band or lower frequency bands (i.e., below 500 MHz) often utilize longer antenna lengths to enhance performance when compared to antennae used in higher frequency applications. In addition, the long range signal propagation characteristics of these lower frequencies allow for superior long range communication. Furthermore, since the mounting height of a radio antenna serves to increase its range, radio antennae are commonly mounted from an elevated position (e.g., a tower or mast). As a result, it has been found that radio antennae are highly susceptible to lightning strikes, the high electrical energy of a lightning strike increasing the likelihood of significant damage to any sensitive components connected to the transmission line, which is highly undesirable.
As a result, at least one RF transmission line component is commonly provided with a protective device for suppressing or otherwise deflecting undesirable electromagnetic impulses away from a load connected thereto. For example, it is well known in the art for a coaxial electric device to include a shunt conductor that connects the inner conductor either to a high voltage suppression device, such as one or more gas discharge tubes, or directly to a grounded element, such as the outer conductor. Accordingly, in use, the shunt conductor serves to divert potentially harmful transient voltages away from the transmission line for suppression and/or grounding, which is highly desirable. An example of a protective device provided with a shunt conductor for diverting undesirable impulses away from an RF transmission line is shown in U.S. Pat. No. 7,440,253 to George M. Kauffman, the disclosure of which is incorporated herein by reference.
Electrical devices of the type as described above are also often provided with at least one filtering device for separating from the input signal, inter alia, (i) lower frequency signals (i.e., signals that fall beneath the desired high frequency band) which can ultimately be used as control and/or modem signals, and/or (ii) power (e.g., direct current (DC) power) that can be used to power remote end devices.
Although well known in the art, electrical devices of the type as described above that include protective and/or filtering components typically suffer from at least some of following shortcomings.
As a first shortcoming, electrical devices of the type as described above traditionally include protective and/or filtering devices that are installed in a relatively inaccessible manner. Accordingly, if either the protective or filtering device needs to be accessed over time for replacement or repair (e.g., after a lightning strike), a significant degree of disassembly (and subsequent reassembly) is typically required. Due to the labor-intensive nature of such an action, electrical devices with old or defective components are often discarded and replaced in their entirety, which is highly undesirable from a cost perspective.
As a second shortcoming, electrical devices of the type as described above are typically designed and manufactured with a pre-defined, unmodifiable set of performance capabilities. As a result, traditional electrical devices can not be readily enhanced, or otherwise modified, by the user to acquire additional capabilities. For example, a traditional electrical device that is constructed with high voltage suppression capabilities can not be easily modified by the user to additionally acquire signal filtering capabilities.